In 3GPP (3rd Generation Partnership Project) which is a project aiming to standardize a mobile communication system, the introduction of Device to Device (D2D) proximity service is discussed as a new function after Release 12 (see Non Patent Document 1).
The D2D proximity service (D2D ProSe) is a service in which direct communication is enabled without passing through a network within a synchronization cluster formed by a plurality of synchronized user terminals. The D2D proximity service includes a discovery process (Discovery) in which a proximal terminal is discovered and a communication process (Communication) in which direct communication is performed.